1. Field of the Invention
The present invention relates to a magnetic head that incorporates a sensor for measuring a flying height of the magnetic head and for detecting the presence or absence of a projection on a surface of a magnetic disk, and that is used for writing information on the magnetic disk and/or reading information from the magnetic disk.
2. Description of the Related Art
A magnetic head, such as a hard disk device, is arranged at an interval apart from a surface of a rotating magnetic disk, and functions to write information on the magnetic disk and/or to read information from the magnetic disk. In recent years, in association with high density recording on the magnetic disk, the interval between the magnetic head and the surface of the magnetic disk (a flying height of the magnetic head) has become extremely small. The interval is set at, for example, 10 nm or less. In such a case where the flying height of the magnetic head is very minute, when the flying height of the magnetic head is fluctuated for some reason or there is an unintentional projection on the surface of the magnetic disk, the magnetic head may contact the surface of the magnetic disk, thereby damaging the magnetic head. Therefore, in order to control the magnetic head so as not to contact the magnetic disk, it is desirable to control the flying height of the magnetic head and to preliminarily detect the presence or absence of the projection on the surface of the magnetic disk.
In Japanese Patent Laid-Open Publication No. 2004-164797, a projection detection head having a sensor for detecting a projection formed on a surface of a magnetic disk is disclosed. This sensor is arranged on an air bearing surface of a slider including the projection detection head, and detects a resistance change corresponding to frictional heat generated by contact between the projection detection head and the magnetic disk. Since this configuration is configured with not only the magnetic head but also the projection detection head, the configuration is extremely complex or two devices (a magnetic disk device and the projection detection device) are needed. Therefore, this results in a complex configuration and an increase in cost.
In Japanese Patent Laid-Open Publication No. 1-18-167121, Japanese Patent No. 2953417, and Japanese Patent No. 2980074, another configuration is disclosed. In the configuration, a MR (magneto-resistance) element that actually works as a reproducing element of a magnetic disk device is used as a sensor for detecting a resistance change corresponding to frictional heat generated by contact between a magnetic head and a magnetic disk. In Japanese Patent No. 2953417 and Japanese Patent No. 2980074 among the documents, the MR element is positioned in a stepped-back position from an air bearing surface that is opposite to the magnetic disk, and is connected to a heat conductive film exposed to the air bearing surface.
In the prior art, the presence or absence of the unintentionally formed projection (abnormal projection) on the surface of the magnetic disk is detected, and the sensor does not exercise a special functional effect when a normal magnetic disk is used on which an unintentional projection is not present.
For a sensor for detecting the resistance change corresponding to the frictional heat generated by contact between the magnetic head and the magnetic disk, when such a sensor is away from a portion of the magnetic head which directly contacts the magnetic disk, it is sometimes impossible to detect the contact. However, it is necessary for the reproducing element of the magnetic disk device to be positioned in a suitable position for reproducing information. Accordingly, the reproducing element may not necessarily be positioned at a suitable position as the sensor for detecting the contact. A TMR (tunnel magneto-resistance) element that has been the mainstream of a reproducing element in recent years is not appropriate when the flying height of the magnetic head is small as described above. That is because a change of an electrical resistance value of a barrier layer caused by a change in heat is small so that detection sensitivity is not excellent.
In U.S. Pat. No. 7,589,928, a device is disclosed for measuring a flying height of a magnetic head from the magnetic disk, i.e., an interval between the magnetic head and the surface of the magnetic disk regardless of presence of a projection on a surface of a magnetic disk. In this device, a configuration with a sensor is disclosed in addition to a recording element and a reproducing element of the magnetic head. The sensor is disposed for detecting a temperature change corresponding to a change of the flying height of the magnetic head from the magnetic disk.
In the former of the above-described prior art for detecting the projection on the surface of the magnetic disk, the frictional heat generated by actual contact between the projection detection head or the magnetic head and the magnetic disk is used. Also in the latter of the above-described prior art for measuring the flying height of the magnetic head from the magnetic disk in order to obtain the flying height of the magnetic head under a certain state, an output of the sensor under the certain state and an output of the sensor under a contacting state where the magnetic head is intentionally contacted to the surface of the magnetic head are compared. In other words, by comparing the state where the flying height is to be measured with the other state where the flying height of the magnetic head is zero, the flying height to be measured is obtained. Accordingly, in all of the above-described prior art, the magnetic heads have to be contacted to the magnetic disk.
If the sensor itself directly contacts the magnetic disk when the magnetic head is contacted to the magnetic disk as described above, the sensor might possibly be damaged so that physical reliability is impaired and/or corrosion resistance is deteriorated. The sensor is exposed on the air bearing surface which must be formed with high accuracy in order to increase the accuracy of recording and reproducing while maintaining the magnetic head in the desired orientation and position. If the sensor is largely jutted or stepped-back from the air bearing surface, it is difficult to maintain the air bearing surface in the desired shape so that performance of the magnetic head may be deteriorated. Accordingly, the sensor must be of a size and a shape that does not affect the size and shape of the air bearing surface, and there is a restriction to choose material as well.